Over the course of the past decade, optical networks have evolved from simple single-channel synchronous optical network (SONET) regenerator-based links to multi-span, multi-channel optically amplified ultra-long-haul transport systems, necessitated by the high demand for increased bandwidth at a reduced cost. Typically, the cost of a well-designed high-capacity transport system is dominated by the number of optical-to-electrical (OE) and electrical-to-optical (EO) conversions that are required. As the reach and channel capacity of such transport systems continues to increase, it became necessary at some point to improve the granularity of the demand connections by introducing optical add/drop multiplexers (OADMs). Thus, if a given node requires only small demand connectivity, most of the optical channels are expressed through the node without optical-electrical-optical (OEO) regeneration. Optical network costs are correspondingly reduced, even taking into account the increased costs of the OADMs. More recently, the optical networking industry has been aggressively pursuing a natural extension of this philosophy, moving towards all-optical “analog” core networks, with each demand encountering electrical digital circuitry only at the ingress/egress nodes. Not surprisingly, this is expected to produce a substantial elimination of OEO-related costs, an increase in optical network capacity, and nominally simpler operation and service.
At the same time, such all-optical “analog” core networks require a large amount of complicated hardware and software for monitoring and manipulating the high-bit rate optical signals that they carry. New and more complex modulation formats that provide resiliency with respect to both optical noise and nonlinear propagation effects are important for extended un-regenerated reach. More sophisticated optical amplifiers provide lower optical noise for extended reach and increased spectral bandwidth for increased wavelength counts reduce wavelength blocking probabilities. All-optical “analog” core networks also require mechanisms for mitigating optical power transients, controlling spectral flatness, and dynamically managing changes (e.g. in chromatic dispersion (CD) and polarization mode dispersion (PMD)). Because signals now stay in the optical domain, optical performance monitoring techniques are required for fault isolation and correction. The efficient routing of optical signals also requires sophisticated switching nodes with the ability to selectively steer the optical signals towards different directions with single-channel spectral granularity. Most of these technologies are not modular in nature and require an interruption in service if not deployed during initial system installation, thereby increasing initial installation substantially, even if initial capacity loading is small.
As the signal bit rate in an optical network increases, the distortion accumulated by the optical signal increase at a high rate. For example, CD may severely affect the propagating signal by inducing strong group velocity dispersion. Typical 2.5 Gb/s optical signals have a dispersion tolerance of approximately 17,000 ps/nm, which is equivalent to approximately 1,000 km of non-dispersion-shifted fiber (NDSF) at 1,550 nm. Increasing the signal bit rate to 10 Gb/s, as is typical in current optical networks, reduces this dispersion tolerance by a factor of 16 to approximately 1,100 ps/nm, which is equivalent to approximately 65 km of NDSF. Increasing the signal bit rate further to 40 Gb/s, as is expected in state-of-the-art optical networks, reduces this dispersion tolerance by another factor of 16 to approximately 70 ps/nm, which is equivalent to approximately 4 km of NDSF. Other optical signal distortions may be associated with PMD and with nonlinear propagation effects present in the optical fiber.
The validation of systems and software targeting a specific optical network design is complex. Only a small fraction of the optical network may be reproduced and represented at a given time, and many field configurations are dynamic and unpredictable. Thus, extra margin must be allocated to account for behavioral uncertainty. In order to reduce the complexity of both hardware technology and software algorithms, regions of network transparency may be established with optical signal regenerators forced at perimeters. Thus, “analog” regions are surrounded by “digital” regenerator interfaces. Again, the complexity and cost of an optical network may be substantially reduced via the introduction of more frequent, and inexpensive, optical signal regenerators. The present invention achieves this goal and adds additional functionalities to these optical signal regenerators.